This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 2000-261792 filed on Aug. 30, 2000 and Japanese Patent Application No. 2000-300016 filed on Sep. 29, 2000, the entire content of both of which is incorporated herein by reference.
This invention relates to a master cylinder. More particularly, the present invention pertains to a master cylinder used to in a brake device or a clutch device of a vehicle.
An example of a known master cylinder is disclosed in Japanese Patent Laid-Open Publication No. 2000-71969. The master cylinder includes a cylinder housing having an inner bore whose rear end is open, a piston having a bore opening forward and inserted into the inner bore of the cylinder housing, a spring disposed in the bore of the piston, and a retainer disposed between the piston and the spring. The retainer is secured to the rear end of a rod and is inserted to the bottom portion of the bore of the piston. The rod supports a stopper so as to be able to move relative to the stopper and to engage the stopper. The spring is interposed between the retainer and the stopper so that a set length of the spring is set to the total of the length of the rod and the length of the stopper.
However, with the above-described master cylinder, because the retainer, the rod, the stopper and the spring are not united with the piston, the workability from the standpoint of assembling the piston into the cylinder housing deteriorates.
An example of a master cylinder in which a retainer, a rod, a stopper and a spring are united with a piston is disclosed in Japanese Patent Laid-Open Publication No. 10 (1998)-44967. In this master cylinder, an expanded annular groove is formed on an inner circumferential surface adjacent to the bottom portion of a bore of the piston. An expanded diameter portion formed on the outer circumferential portion of the spring or an outer circumferential portion of the retainer is engaged with the expanded annular groove. However, in this master cylinder, because the expanded annular groove has to be formed on the inner circumferential surface of the bore of the piston, the machining for the bore of the piston is complicated and so the machining cost is increased. Further, air is apt to stay in the expanded annular groove.
Another example of a master cylinder in which a rod, a stopper and a spring are united with a piston is disclosed In U.S. Pat. No. 6,012,288. In this master cylinder, the retainer is omitted and the rear end portion of the rod is fitted into a fitting hole which is formed on the bottom portion of the bore of the piston. However, in this master cylinder, because the fitting hole has to be formed on the bottom portion of the bore of the piston, the machining cost for the bore of the piston is increased. Further, the axial length of the piston required to form the fitting hole is increased and so it is difficult to miniaturize the master cylinder.
It would thus be desirable to provide a master cylinder which is not as susceptible to the disadvantages and drawbacks discussed above.
A need exists for a master cylinder in which a retainer, a rod, a stopper and a spring can be united with a piston without increasing the machining cost of the piston and without increasing the axial length of the master cylinder.
A master cylinder includes a cylinder housing having a rearwardly opening inner bore, a piston having a forwardly opening bore opened and positioned in the inner bore of the cylinder housing, a spring disposed in the inner bore of the piston, a stopper supporting a front end of the spring, a retainer disposed in the inner bore of the piston and supporting a rear end of the spring, and a rod connecting the retainer and the stopper while allowing the spring to compress in the axial direction. A plurality of projection portions are formed on the outer circumferential portion of the retainer and the retainer is pressed into the inner bore of the piston via the projection portions.
According to another aspect of the invention, a master cylinder includes a cylinder housing having an inner bore that is open at a rearwardly facing end of the cylinder housing, a piston positioned in the inner bore of the cylinder housing and having a bore that is open at a forwardly facing end of the piston, a spring disposed in the bore of the piston, a stopper supporting a front end of the spring, and a retainer disposed in the bore of the piston and supporting a rear end of the spring. The retainer is disc-shaped and possesses a plurality of circumferentially spaced apart and radially outwardly directed projecting portions that engage an inner surface of the bore in the piston. A rod extends between the retainer and the stopper in a manner that allows the spring to be axially compressed.